The project is to entail research in the following areas: 1. Attempts to reproduce in vitro the entire life cycle of Trypansoma brucei subspecies through the use of Hirumi's (1977) system for the cultivation of bloodstream forms and of Cunningham and Honigberg's (1977) SM medium tsetse fly head-salivary gland system for the production of metacyclic stages. 2. The use of the aforementioned in vitro systems for analysis of the various factors that may affect antigenic variation of the bloodstream forms of T. brucei subspecies. 3. Search, in cultures, for the environmental factors that affect the formation of metacyclic forms and the antigenic analysis of these stages primarily by the fluorescent antibody methods. 4. Continuation of experiments involving cyclical transmission of T. b. brucei through the vector to establish, by antigenic analysis, the relevance of transmission by in vitro-produced metacyclic forms to transmission by vector-produced infective trypanosomes. 5. Studies, by ultramicrofluorometry, of the antigenic composition of surfaces of T. brucei subspecies and T. congolense developmental stages, including bloodstream forms, and of the antigenic changes occurring in the course of the bloodstream-to-procyclic form and proventricular-to-metacyclic form transformations in vivo and in vitro. 6. Further characterization of the nonvariant antigen shared by T. b. brucei bloodstream forms and testing the immuno-protective potential of this antigen in laboratory rodents. 7. Continuation of immunologic and biochemical analyses of the Leishmania donovani exometabolites and testing of the effect of these substances on the course of infection in laboratory hosts. 8. Further antigenic analysis of the thermally adapted substrain of L. donovani 3S strain.